Theorem 1
Tag 00Y2, permanent. Cite it as [Bourbaki, Tag 00Y2].
Lie Groups and Lie Algebras, chapter VIII, § 1. The Lie algebra sl(2, k) and its representations
Every simple -module of finite dimension is isomorphic to . Every finite dimensional -module is a direct sum of submodules isomorphic to the modules .
This follows from Lemma 4 and Prop. 1, 2 and 3.
Bourbaki sets the proof directly after the statement, and the corpus does not separate them, so what is above is the statement and its proof together.